Corylus avellana

The common hazel is in the birch or Betulaceae family and is native to Europe and western Asia. It has been cultivated over the centuries for its nuts, still supplying most of the hazelnuts grown today. It is typically a multi-stemmed shrub reaching up to 8 m tall, but can grow to 15 m.

In North America, the eastern filbert blight has decimated many of the common hazel trees. Some farmers are now replanting with blight-resistant varieties of C. avallana.

'Harry Lauder's Walking Stick' is a contorted variety of C. avellana which has been developed for its attractive twisting branches. It forms a dense shrub 6 m or more in height.

• Leaves are deciduous, alternate, simple, rounded, 6–12 cm long and across, softly hairy on both surfaces, and double-toothed. New growth in the spring is covered with sticky hairs. Common hazel often stands out with its patches of multiple stems.
• The species is monoecious. Male flowers form catkins that are pale yellow and 5–12 cm long, notably visible in mid-winter before the leaves of most species are out. Females are very small and largely concealed in the buds with only the bright red 1–3 mm long styles visible.
• Fruit is a nut, produced in clusters of 1–5, each nut in a short leafy involucre (husk) that covers over half the nut. Nut is spherical to oval, 15–20 mm long and 12–20 mm broad, with different varieties being larger or smaller. Nuts are yellow-brown with a pale scar at the base.
• The common hazel used commercially for growing hazelnuts is self-unfruitful, which means its blossoms must be fertilized with the pollen from a different variety in order to achieve good fruit set. This is similar to many fruit trees which are self-unfruitful to some degree or to a large degree.